Three types of apparatus are nowadays in use for taking routine measurements of human temperature in hospitals: analogous, electronic and infrared clinical thermometers.
The conventional analogous liquid-glass clinical thermometers operate on the basis of the temperature-dependent expansion of a liquid metal, specifically mercury. Measurements may be taken in the axilla, mouth or rectum. Reading the measured temperature value and resetting the thermometer by shaking the thermometer is usually done by medical personnel. These thermometers are inexpensive, and, due to the glass body, may be disinfected without problem. Disadvantages, however, reside in the fragility of the body, in the relative poor readability of the measurement results, and in the frequency such thermometers are stolen by patients and clinical personnel.
Compact electronic clinical thermometers operate on the basis of the temperature-dependent change of resistance of a thermistor. These thermometers have a body of plastics material. These thermometers also permit measurements to be taken in the axilla, mouth or rectum. Prior to taking a measurement, the medical personnel is required, for hygienic reasons, to provide thermometers of this type with a cover. This causes additional cost and produces special refuse. The thermometers are almost unbreakable, well readable and only little more expensive than analogous clinical thermometers. However, they also are frequently stolen.
Infrared clinical thermometers measure the temperature-dependent radiation of the tympanic membrane. They operate fast but are available for measurements in the ear only, and the medical interpretation of the measurement result is not always without problem. Again, hygienic considerations require these thermometers to be provided with a fresh protective cover prior to every measurement. Placing the thermometer at the measurement location requires trained personnel and may, in case of repeated measurements, cause injure and pain. Clinical thermometers of this type are less suited for private use and, as a consequence, are not stolen. They are, however, substantially more expensive than analogous and electronic clinical thermometers.
Specific methods of electronically measuring the body temperature involve telemetric systems, such as are known from DE 3 219 558 A1, DE 4 441 083 C1, U.S. Pat. No. 4,503,862, and U.S. Pat. No. 4,865,044. These systems include a measuring probe (the thermometer proper) to be disposed on or in the patient and a separate evaluation unit.
In the system of DE 3 219 558 A1, a micro probe is implanted in the body and supplied with energy for the measurement by means of a high frequency field. The transmission of the measured value is done by absorption modulation of the HF field. Due to the small size of the measuring probe, it is difficult to supply the probe with the energy required for the measurement and for the transmission of the measured value. It is therefore necessary to expose the patient to a very strong electromagnetic field. The measuring probe is switched on and off by turning on and off the HF field. Measured values can be transmitted only when the probe is on the patient. The system is unsuited for routine measurements in a hospital.
In the system according to DE 4 441 083 C1, a telemetric measuring probe is included in an adhesive plaster which is placed on the desired location of the patient""s skin. In addition to the fact that this type of placement is unsuited for measuring body temperatures at the usual locations, the patient""s skin is unnecessarily irritated by the possibly repeated application and removal of plasters as would be required for taking routine measurements. Also, undesired special refuse is produced. Further, changing the plaster involves work for the nursing personnel. The provision of a largesize antenna in the form of a pillow to be placed under the patient, as recommended in this document, is expensive and hardly practical for hygienic reasons. Also, the measuring probe operates in this system only within a high frequency field and yields meaningful measurement results only if the probe is placed on the patient.
U.S. Pat. No. 4,503,862 describes a system in accordance with the first part of claim 1, wherein each patient is given his own battery-powered measuring sensor. On her round, the nurse carries a receiver unit from one patient to the next and actuates the transmitter of the respective sensor next to the receiver unit to transmit the detected temperature value. This process must be repeated for every individual. patient. As a disadvantage of this system, the sensor produces correct measurement results only if placed on the patient. The detected data must be allocated to the individual patients manually, e.g. by means of a listing.
The temperature monitoring system proposed in U.S. Pat. No. 4,865,044 uses a plurality of telemetric sensors. When a predetermined threshold value is exceeded, these sensors transmit continuously and in predetermined intervals their identification number and a modulated signal which corresponds to the measured temperature. As a disadvantage, once the starting condition has been reached, the sensors transmit continuously irrespective of whether the receiver unit is turned on and whether the sensors are within the range of the receiver unit. To save energy, it has been proposed to turn on and off the sensors periodically. When the period is relatively short, updated measurement values may be obtained virtually continuously, but this results in a high energy consumption. A long period reduces the energy consumption, but the waiting time until the moment the next actual measurement value is received may become relatively long. Since no provision is made to collect the detected temperature data selectively, the system is unsuited for routine temperature measurements in hospitals.
It is a general object of the invention to provide a medical telemetry system for vital data, specifically for taking routine measurements of the body temperature, which system avoids the disadvantages of the prior art explained above. A more specific object may be considered to reside in permitting measurement of the body temperature at the usual measurement locations at low expenses, (i.e. low cost per measurement), minimum labor for the nursing personnel, maximum safety of the data, and high comfort for the patient.
This object is met by the medical telemetry system set forth in claim 1. In the system according to the invention, the individual measuring sensors continuously and automatically monitor a predetermined threshold value and start a measurement when this threshold value is exceeded. The measured value is stored in the sensor and transmitted upon request from a collecting device.
When admitted to a hospital, every patient is given his own measuring sensor. Within an agreed period of time, the patients place their personal measuring sensor at the intended measuring location. When the measurement has been taken, the patient can remove the measuring sensor from the measuring location and store it in a holder provided for this purpose. Even after the measurement, the sensor remains active over a defined period of time during which it stores the measured value and transmits it upon receipt of a request signal. Nursing personnel is required only for collecting the measurement values stored in the measuring sensors, which is done by means of a collecting device that needs to be taken only close to the individual measuring sensors in order to collect the measured value telemetrically upon transmission of the request signal. There is thus no need to touch either the patient or the sensor, which is of advantage particularly in case of highly contagious diseases. Moreover, it is not at all necessary for the patient to be present at the time the measured value is collected. Since the measuring sensor has no display of its own, it is useless as a measuring device for private purposes, which should have a great influence on the disappearance of thermometers in hospitals.
The embodiment of claim 2 is useful because the patient does not have to place the measuring sensor into operation, and there is the additional advantage that no mechanical keys or switches with corresponding openings in the sensor body are required. This improves especially the hygienic properties of the sensor body.
The embodiment of claim 3 realises a maximum thermometer system as is common for routine temperature measurements.
The embodiment provided in accordance with claim 4 offers high comfort for the patient who needs to leave the measuring sensor at the measuring location for only a minimum period of time.
The feature of claim 5 can be useful in that measured values can be evaluated in minimum time.
The ID code of claim 6 which is transmitted along with the data ensures a unique and unambiguous association of the measurement results received by the collecting device to the individual patients.
In accordance with claim 7, since the values, which are not collected within a predetermined period of time, are cleared, confusion between xe2x80x9coldxe2x80x9d and xe2x80x9cnewxe2x80x9d measured values is safely excluded. In accordance with claim 8, the erasing can be done immediately upon the transmission of the respective measured value.
The embodiment of the invention in accordance with claim 9 has the advantage that the outer appearance of the measuring sensor corresponds to that of a conventional clinical thermometer so that the patients have no difficulty to take their own measurements as usual. At the same time, the thermometer body is suited for receiving a sufficiently powerful battery and powerful antenna, which is of advantage for the signal transmission.
The development of the invention set forth in claim 10, according to which the sensor is shaped so that the sensor body can be sterilised when changing the patient, improves the hygienic aspect when taken routine measurements of the body temperature in a hospital.
Claims 11 and 12 relate to the possibility of transmitting and displaying, on the collecting device, information concerning the condition of the individual sensors in addition to the measured values proper. This information chiefly includes the charging condition of the battery. When the voltage drops below a critical value, the user is given information that the battery must be changed. In addition to this status information, it is possible to transmit, e.g., a reference count characteristic of the overall function of the measuring sensor. If this count changes towards values outside a range defined as normal, malfunction of the device may be displayed in any suitable way, e.g. on a display of the collecting device.
The further developments of the invention set forth in claims 13 to 15 result in further reduced labor for the nursing personnel.